Cell surface heparan sulfate proteoglycans are widely distributed throughout animal tissues, and are involved in critical cell-functions such as cell-cell and cell-extracellular matrix interactions. Their interaction with a variety of molecules including growth factors, viruses, and extracellular matrix proteins, have important biological functions. The purpose of this project is to study the metabolism of cell surface heparan sulfate proteoglycans with focus on mechanisms involved in their endocytosis and subsequent intracellular processing. We have studied intracellular localization of heparan sulfate proteoglycan (HSPG) and dermatan sulfate (DS) PGs in an osteoblastic cell line (UMR 106), oral epithelial cells and retroocular fibroblasts using metabolic radiolabeling experiments in combination with subcellular fractionation techniques and examination with electron microscopy. Results indicated that a large proportion of HSPGs formerly identified in nuclear fractions are contamination from plasma membranes and that the small DSPG (probably biglycan and/or decorin) which associates with the cell surface may well traffic through the nucleus in these cells. We also studied biosynthesis of bone sialoprotein (BSP) by a human osteoclastic cell line (FLG 29.1) during its differentiation induced by TPA using metabolic radiolabeling experiments. Topics of present interest include: (1) the study of mechanisms regulating expression of cell surface HS proteoglycans in various cell types, and (2) interactions of cell surface proteoglycans with growth factors, chemokines and viruses.